Rail infrastructure owners are motivated to minimize staff exposure to unsafe environments and replace the time consuming and subjective process of manual crosstie (track) inspection with objective and automated processes. The motivation is driven by the desire to improve rail safety in a climate of increasing annual rail traffic volumes and increasing regulatory reporting requirements. Objective, repeatable, and accurate track inventory and condition assessment also provide owners with the innovative capability of implementing comprehensive asset management systems which include owner/region/environment specific track component deterioration models. Such rail specific asset management systems would yield significant economic benefits in the operation, maintenance and capital planning of rail networks. A primary goal of such automated systems is the non-destructive high-speed assessment of railway track infrastructure. Track inspection and assessment systems currently exist including, for example, Georgetown Rail (GREX) Aurora 3D surface profile system and Ensco Rail 2D video automated track inspection systems. Such systems typically use coherent light emitting technology, such as laser radiation, to illuminate regions of the railway track bed during assessment operations.
The effect of variations in surface properties of railroad tracks and surrounding surfaces has a significant impact on light levels reflected from these surfaces and subsequently detected by 3D sensors. Reflected light levels entering the sensors are not always optimum due to variations surface color (light or dark colored surfaces) or texture for example. Incorrect lighting levels can cause the 3D track surface profile measured by a 3D sensor to be distorted or imperceptible, affecting the measured profile accuracy.
In such systems, high power laser light sources may be used. Laser line projectors may include high power (Class IV) non-visible infrared laser sources (for example; a wide fan angle (75-90°) laser with a wavelength of 808 nm and a power of 10 watts). All Class IV lasers present an extreme ocular exposure hazard when used without external eye protection. Further complicated by the non-visible nature of infrared radiation (deactivating the natural aversion reflexes such as protective pupil contraction, blink, or head turn), Class IV lasers are capable of causing severe eye damage through direct, or reflected light exposure. Reflected exposure occurs when the laser radiation is scattered from highly reflective specular (shiny) targets such as polished metal surfaces (for example in the track environment; rail heads, switches, frogs). In environments where specular reflections are possible, any potential occurrence of exposure must be removed by eliminating ocular access to the beam. Beam access can be restricted by either requiring that protective eyewear (appropriately filtered) be worn by all those with any exposure potential, or by effectively enclosing the beam.
For rail testing environments with moving surveys using Class IV lasers, the top of the rail head presents a nearly ideal continuous omnidirectional specular reflector. In addition to the rail head, other flat or otherwise smooth surfaces (plates, switches, frogs, the materials between and around the rail head near crossings in urban areas), create conditions where the Maximum Permissible Exposure (MPE) limits for ocular damage are exceeded (especially in situations where those surfaces are wet). Adding to the danger of reflected laser energy, the non-divergent nature of laser sources guarantees that any reflected coherent laser light will present an ocular danger for large distances from the reflecting surfaces.
What is needed, therefore, is a way to control high powered light emitters used in systems similar to those described above in real time in order to limit unnecessary exposure to light emitted from such light emitters.